This term is used to describe someone who thinks they know everything yet are often wrong. They will argue and lie to be right. Often get louder when challenged. It can also be said they have shit for brains. Often offer unnecessary information just to have something to say.

Said to someone who is the offender."You know Jack shit about everything shit for brains".

1) Traditionally refers to drawing Jack-Deuce as your starting hand, ie. "Jack-Shit"; a bad hand. Although may sometimes be extended to refer to a combination of a Jack with any low value card 2-7, typically.

2) Jack-Shit Poker - A variation on the familiar Seven-Deuce Hold'em. A pre-arranged additional reward is owed by one's opponents if he wins a hand with Jack-Deuce as his hole cards.